Skip ActiveJob reloading callback in test env

Because we run ActiveJob inline in test env, there is probably no need
to have code reloading for this while specs are running. This removes
frequent calls to FileUpdateCheker#updated? which is slow on macOS.

config/initializers/remove_active_job_execute_callback.rb

+# frozen_string_literal: true
+
+return unless Rails.env.test?
+
+Rails.application.configure do
+  config.after_initialize do
+    # We don't care about ActiveJob reloading the code in test env as we run
+    # jobs inline in test env.
+    # So in test, we remove this callback, which calls app.reloader.wrap, and
+    # ultimately calls FileUpdateChecker#updated? which is slow on macOS
+    #
+    # https://github.com/rails/rails/blob/6-0-stable/activejob/lib/active_job/railtie.rb#L39-L46
+    def active_job_railtie_callback?
+      callbacks = ActiveJob::Callbacks.singleton_class.__callbacks[:execute]
+
+      callbacks &&
+        callbacks.send(:chain).size == 1 &&
+        callbacks.first.kind == :around &&
+        callbacks.first.raw_filter.is_a?(Proc) &&
+        callbacks.first.raw_filter.source_location.first.ends_with?('lib/active_job/railtie.rb')
+    end
+
+    if active_job_railtie_callback?
+      ActiveJob::Callbacks.singleton_class.reset_callbacks(:execute)
+    end
+  end
+end

spec/initializers/remove_active_job_execute_callback_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'ActiveJob execute callback' do
+  it 'is removed in test environment' do
+    expect(ActiveJob::Callbacks.singleton_class.__callbacks[:execute].send(:chain).size).to eq(0)
+  end
+end